This invention is in the field of reflector lamps, such as those which include the commonly known reflector (R) lamp used for floodlighting and has spotlights.
Reflector (R) lamps are disclosed in U.S. patent application Ser. No. 612,778, filed May 22, 1984, now U.S. Pat. No. 4,536,834, assigned to the same assignee as the present invention and herein incorporated by reference. The U.S. Pat. No. 4,536,834 discloses R lamps having reflective surfaces and an improved neck portion which increases the useful light output of the R lamp.
The prior art R lamps, such as that disclosed in U.S. Pat. No. 4,536,834, have a definite overall length so as to accommodate the physical and optical characteristics of existing lighting fixtures when so inserted.
A prior art reflector lamp may be of the large blown family which type lamp is defined as having a maximum diameter of at least 2.5 inches and whose beam pattern is projected along the center axis of the lamp. The dome of the bulb of this reflector lamp may be defined as the region between the maximum diameter of the bulb and the apex of the "lens" end of the bulb. The dome height may be defined as the vertical distance from the widest or maximum diameter of the bulb to the apex of the lens end. The dome may or may not be implemented to help modulate or disperse the light projected from the lamp. The height of the dome, however, does not aid the optical performance of the lamp and therefore could be reduced without any detrimental effect to the lamp performance.
It would be desirable to completely eliminate the dome height which would make for a flat dome reflector lamp. The flat dome would allow for an increase in the length of the uppermost or primary reflective section having a reflective coating on its inside surface without a corresponding increase in the overall length of the lamp. An increased primary reflection length would improve the directional performance of the projected light beam by redirecting otherwise wasted light rays back into the useful beam pattern of the lamp. Although desirable, it is not practically feasible to provide a lamp having a flat dome due to other considerations.
The bulb during the manufacturing of the lamp and throughout the service life of the lamp may see a net, uniform, external pressure or other external loads. The flat dome contour substantially reduces the structural integrity of the bulb to this loading situation. Hence, the flat dome bulb would most likely pose a problem both from a manufacturing and usage standpoint given that the flat dome bulb might implode. Accordingly, the dome needs some curvature in order to maintain the bulb's structural integrity to the aforementioned pressure-load situation.
Prior art reflector lamps primarily in order to maintain the desired structural integrity have predominately utilized a dome contour consisting of two radii. There are also reflector lamps with dome contours consisting of more than two radii, for example, the elliptical reflector lamps utilize a number of main radii and fillet radii in the dome contour. There are also other reflector lamps with relatively long dome heights which utilize more than two radii in the dome contour. The known prior art elliptical and long height dome reflector designs have a dome height to maximum diameter ratio of greater than 0.24. For a given maximum diameter, it is desired that this ratio be reduced in order that the height of the dome be reduced to allow for an increase in the reflector length which thereby increases the useful light output of the reflector lamp. This ratio reduction should be accomplished while still maintaining the structure integrity of the dome section and also maintaining the overall length of the lamp.
Accordingly, an object of the present invention is to provide a reflector lamp having a dome section which is reduced in height relative to prior art lamps so as to provide more useful light output while still maintaining the structural integrity of the dome and also the overall length of the reflector lamp itself.